Fullerene based proton conductive materials

ABSTRACT

A fullerene-based proton conductor including a proton conductive functional group connected to the fullerene by an at least partially fluorinated spacer molecule. Also, a polymer including at least two of the proton conductors that are connected by a linking molecule. Further, an electrochemical device employing the polymer as a proton exchange membrane, whereby the device is able to achieve a self-humidifying characteristic.

CROSS REFERENCE TO RELATED APPLICATIONS

The present application is a divisional of U.S. patent application Ser.No. 10/986,551, filed on Nov. 10, 2004 now U.S. Pat. No. 7,198,863 whichis a divisional of U.S. patent application Ser. No. 10/115,109, filed onApr. 1, 2002, now U.S. Pat. No. 6,890,676 herein incorporated byreference. The present application claims priority to Japanese PatentDocument P2002-028642 filed on Feb. 5, 2002, herein incorporated byreference.

BACKGROUND

The present invention relates to a proton conductor, a production methodthereof, a polymer made of proton conductors, methods of making thepolymer, and an electrochemical device using the polymer of protonconductors.

One of the most widely used proton conductors is Nafion, which is aperfluorinated sulfonic acid functionalized polymer. The structure ofNafion is shown in FIG. 3, and can essentially be divided in twosubstructures: i) a perfluorinated linear backbone 12; and ii)perfluorinated side chains 14 bearing sulfonic acid functions, i.e., theproton delivering sites. It combines an acceptable proton conductivitywith an extreme inertness against chemical as well as thermalinfluences.

In addition, known fullerene compounds include, for example, compounds 1through 6 (see FIGS. 4A-F) bearing acidic functional groups likesulfuric acid esters (—OSO₃H) or sulfonic acid groups (—SO₃H) that arecapable of conducting protons within their solid-state structure. Theseproton-delivering sites can either be attached directly to the fullerenecore or via various spacer molecules. Depending on the amount of watercontained within the crystal, these compounds show proton conductivitieshigher than 10⁻² S/cm. However, these fullerene-based materials sufferfrom several disadvantages. The most striking one is a lack ofresistance to thermal and/or chemical decomposition. As an example, thebutyl-linked fullerosulfonic acid (compound 6, FIG. 4F) first starts todecompose at about 100-110° C. Yet, thermal and chemical stability areprerequisites for any compound used in a fuel cell application.

Accordingly, there exists a need to provide materials that can beeffectively and readily made and used as proton conductors for a varietyof difference applications.

SUMMARY

One advantage of the present invention is to overcome the above-noteddisadvantages in the related art. More particularly, it is an advantageof the present invention to provide a proton conductive compound thathas high proton conductivity, and that is thermally as well aschemically stable under conditions found in a fuel cell.

Another advantage of the present invention is to provide a protonconductor having an increased proton conductive performance.

Still another advantage of the present invention is to provide afullerene-based proton conductive material that is thermally andchemically stable under conditions found in a fuel cell. Moreparticularly, it is an advantage of the present invention to provide afullerene-based proton conductive material that has a thermal stabilityon the order of 200° C. as measured by temperature programmed desorption(TPD), whereby it can be used in an application environment of about 80°to about 90° C. over a practical useful lifetime.

Yet another advantage of the present invention is to provide methods ofmanufacturing the above-described proton conductor, as well as a polymerfilm thereof. And another advantage of the present invention is toprovide an electrochemical device having an acceptable conductance, selfhumidifying characteristics, as well as an increased thermal andchemical stability.

In an embodiment, the present invention attains the above and otheradvantages by connecting a proton conductive functional group to afullerene molecule by a spacer molecule that is at least partiallyfluorinated.

More particularly, the present invention achieves a high protonconductivity because these fullerene-based proton conductors have a highnumber of proton conductive groups per unit of atomic weight. That is,as a non-limiting example, Nafion usually includes one proton deliveringsite per about 1,100 units of atomic weight, whereas a C₆₀ fullerenemolecule carrying an average of ten proton conductive groups wouldincrease this ratio about three times (i.e., it would have an average ofone proton delivering site per about 370 units of atomic weight), whichresults in a considerable enhancement of the proton conductive group toweight ratio.

Further, the fullerene-based proton conductors of the present inventionhave at least a partially fluorinated spacer molecule connecting aproton conductive functional group to the fullerene back bone, wherebythe present invention achieves a higher thermal and chemical stabilitythan that of the previous fullerene-based proton conductors known withinApplicants' company.

Moreover, in an embodiment, the above-noted advantages of the inventionare achieved by providing a proton conductor comprising:

a fullerene molecule;

a spacer molecule attached to said fullerene molecule, wherein saidspacer molecule is an at least partially fluorinated molecule; and

a proton conductive functional group attached to said spacer molecule.

The above-noted advantages of the invention also are achieved byproviding a polymer comprising:

a plurality of proton conductors as set forth above; and

at least one linking molecule connected between two of the plurality ofproton conductors.

Additionally, in a further embodiment, the above-noted advantages of theinvention are achieved by providing a method of making a protonconductor, comprising:

a first step of combining a fullerene with a spacer-molecule precursorto form a first reaction product, wherein the spacer-molecule precursoris at least partially fluorinated;

a second step of hydrolyzing the first reaction product so as to form asecond reaction product; and

a third step of protonating the second reaction product so as to form aproton conductor that includes a proton conductive functional groupattached to said fullerene by a spacer molecule that is formed from saidspacer-molecule precursor and that is at least partially fluorinated.

Further, in an additional embodiment, the above-noted advantages of theinvention are achieved by providing a method of making a protonconductive polymer film, comprising the steps of

a first step of combining fullerenes with spacer-molecule precursors toform a plurality of first reaction products, wherein each of thespacer-molecule precursors is at least partially fluorinated;

a second step of combining the first reaction products withlinking-molecule precursors so as to form second reaction products,wherein each of the second reaction products includes at least two ofthe first reaction products that are connected by a linking moleculeformed from one of the linking-molecule precursors; and

a third step of protonating the second reaction products so as to form anetwork of proton conductors that each includes a proton conductivefunctional group attached to the fullerene by a spacer molecule that isformed from the spacer-molecule precursor and that is at least partiallyfluorinated.

Lastly, in an embodiment, the present invention achieves anelectrochemical device having an increased thermal and chemicalstability, by employing therein a proton exchange membrane including theabove-described proton conductor.

Additional features and advantages are described herein, and will beapparent from, the following Detailed Description and the figures.

BRIEF DESCRIPTION OF THE FIGURES

FIGS. 1A-D show various examples of proton conductors according to anembodiment of the present invention.

FIG. 2 is a schematic representation of a fuel cell according to anembodiment of the present invention.

FIG. 3 is a schematic diagram showing the structure of a protonconductive material known in the art.

FIGS. 4A-F show various fullerene-based proton conductive known in theart.

FIG. 5 is a schematic representation of a method for the polymerizationof a proton conductor according to an embodiment of the presentinvention.

FIG. 6 is a schematic representation of a method for the polymerizationof a proton conductor or by a one-pot reaction according to anembodiment of the present invention.

FIG. 7 is a schematic representation of another method for polymerizingby an additional step according to an embodiment of the presentinvention.

FIG. 8 shows the change in proton conductivity of perfluorohexylcross-linked materials under a water saturated air stream at 19° C.according to an embodiment of the present invention.

FIG. 9 shows the change in proton conductivity of perfluorohexylcross-linked materials under a water saturated air stream at 50° C.according to an embodiment of the present invention.

FIG. 10 shows the change in proton conductivity of perfluorohexylcross-linked materials at various temperatures according to anembodiment of the present invention.

FIG. 11 is a comparison of the change in proton conductivity ofperfluorohexyl cross-linked materials based on C₇₀, C₆₀, and Nafionaccording to an embodiment of the present invention.

DETAILED DESCRIPTION

The present invention is embodied in a fullerene molecule havingattached thereto at least one spacer molecule that, in turn, is attachedto a proton conductive functional group. There may be more than onespacer molecule and more than one proton conductive functional group perfullerene. Further, although it is more usual to have each of the spacermolecules and each of the proton conductive functional groups be thesame on each fullerene, such is not necessary. That is, each fullerenemay include a plurality of different spacer molecules. Similarly, aplurality of different proton conductive functional groups may beattached to a fullerene by the same type, or a different type, of spacermolecule.

In general, a fullerene is a molecule made of carbon atoms and having amore or less spherical shape. As the fullerene molecule in the presentinvention, any of the known fullerene molecules can be used. Forexample, fullerenes are exemplified by C₃₆, C₆₀, C₇₀, C₇₆, C₇₈, C₈₂,C₈₄, C₉₀, C₉₆, etc., all the way to C₂₆₆. Presently, because they arereadily commercially available at a reasonable price, and generallybecause as the fullerene size increases its reactivity decreases, C₆₀and C₇₀, or a mixture thereof, are the preferred fullerenes. The use offullerene molecules provides an increased mobility of protons becausethe fullerene molecules have a uniform shape that is independent fromthe direction in which the proton carriers are moving, thereby leadingto a high proton conductive performance in the present invention.Further, the present invention achieves a high proton conductivitybecause the fullerenes have a high number of proton conductive groupsper unit of atomic weight.

Although not necessary, the fullerene molecule may have attached theretoadditional functional groups such as, for example: halides (F, Cl, Br);alkyl and/or aryl groups; fully, partially, or non, fluorinatedhydrocarbons; or other functional groups, such as ethers, esters,amides, ketones, and other suitable materials. These additional groupsmay have a stabilizing impact on the material as, for example, againstradicals present in a fuel cell device. Also, these additional groupsmay cause an enhancement of the proton conductivity through effectscaused by the electro negativity of the fluorine atoms, and/or throughthe segregation of water contained in the solid into the hydrophilicareas around the acetic groups away from the hydrophobic fluorinatedparts. However, the presence of these additional functional groupsreduces the number of spacer molecules that can be attached to thefullerene and, in turn, reduces the number of proton conductivefunctional groups that may then be attached thereto. Therefore, it ispreferred that the fullerene molecule not have such additionalfunctional groups attached thereto, whereby the number of spacermolecules, and thus proton conductive functional groups, can beoptimized. However, because the proton conductor of the presentinvention is largely water soluble as a molecule, it is beneficial toform a polymer by cross-linking the fullerene molecules that have thespacer molecules and the proton conductive groups attached thereto.Therefore, the number of spacer molecules attached to the fullerenemolecule must be balanced with the need also to attach linking moleculesthereto in order to form a cross-linked polymer, as discussed later.

A spacer molecule of the present invention may be an alkyl or aryl, andis at least partially fluorinated. It is the presence of an at leastpartially fluorinated spacer molecule that gives the overall protonconductor its increased thermal and chemical stability. In a preferredembodiment of the present invention, the spacer molecule is a fully, orpartially, fluorinated compound including, for example, hydrocarbonchain or combination thereof that may include other atoms, or groups. Asa non-limiting example, a spacer molecule of the present invention mayinclude: a partially fluorinated hydrocarbon chain; a perfluorinatedhydrocarbon chain; (C_(n)F_(2n)), wherein n is a natural number; apartially, or fully, fluorinated aromatic structure (i.e., thefluorinated portion of the spacer need not be restricted to the CF₂alkyl type); or CF₂—CF₂—O—CF₂—CF₂, as shown in compound 7 of FIG. 1A.Generally, the more fluorine atoms in a spacer molecule, the more stableit will be, but stability also depends on the position of the F and Hatoms in the case of partial fluorination. Presently, CF₂—CF₂—O—CF₂—CF₂is preferred because it is very stable, and is readily commerciallyavailable. However, partially fluorinated spacers may be advantageousbecause they may be less costly than their perfluorinated counterparts,and may offer sufficient stability for use in a fuel cell. That is, forexample, as shown in FIGS. 1B-D, a spacer molecule may include: anon-fluorinated spacer portion having a CF₂ molecule on each of itsends, as in compound 8, FIG. 1B; a non-fluorinated spacer portionconnected between a fullerene and a CF₂ molecule, as in compound 9, FIG.1C; or a non-fluorinated spacer portion connected on one of its ends tothe fullerene by a CF₂ molecule whereas it is connected directly to aproton conductive group on its other end, as in compound 10, FIG. 1D.Additionally, a spacer molecule of the present invention may include,optionally attached thereto, other functional groups such as, forexample, ethers, esters, ketones, or combination thereof.

A proton conductive function group of the present invention may be anyof the known proton conductive function groups. More specifically, aproton conductive function group of the present invention may be: anacidic function group; a sulfuric acid ester; a sulfonic acid group; aphosphoric acid ester; or a carboxylic acid group; or a sulfonamide(—SO₂NH₂), or other suitable compounds. Generally, however, the strongerthe acid, the better. Therefore, the sulfonic acid group is preferred.

The proton conductors of the present invention can be made by anysuitable process. The following is an exemplary process for synthesizingthe proton conductors of the present invention.

In general, a fullerene is first combined with a spacer-moleculeprecursor to form a first reaction product. Generally, thespacer-molecule precursor includes a docking end that attaches to thefullerene molecule, and a functional-group-precursor end on which theproton conductive functional group will eventually be formed. Then, thefirst reaction product is hydrolyzed, resulting in a second reactionproduct for accepting protons. Lastly, the second reaction product isthen protonated to yield a third reaction product that is the targetcompound, i.e., the proton conductor of the present invention.

More specifically, but still as a non-limiting example, the followingprocess steps may be followed to synthesize the proton conductors of thepresent invention.

First, a fullerene is combined with a spacer-molecule precursor in asolvent. In general, the spacer-molecule precursor is of the formula:X—R_(F)—Y,

wherein:

-   -   X is Cl, Br, or I;    -   RF is a fully, or partially, fluorinated spacer. Further, it may        contain attached thereto other functional groups such as ethers,        esters, phosphoric acid esters, and/or carboxylic acids; and    -   Y is a functional group that will undergo further reaction to        transform it into a proton conductive functional group.

Also in general, the solvent mixture is such that it is capable ofdissolving the desired reaction product, but not of readily dissolvingthe fullerene and low adducts, whereby the desired reaction product mayeasily be separated from the side products and unreacted fullerene byfiltering or centrifuge techniques.

The fullerene, spacer-molecule precursor, and solvent, mixture is thensubject to a predetermined activation energy, such as a predeterminedreaction temperature for a predetermined reaction time. Thepredetermined activation energy may be supplied by any suitable methodsuch as, for example, by heating, by application of light (either UV orvisible), and the like. A first reaction product is produced by thecombination of the spacer-molecule precursor and the fullerene. That is,the general formula of the first reaction product is--fullerene-R_(F)—Y-- (as used herein, double hyphens are used to offsetdescriptive chemical designations). The unreacted fullerene, and anyunwanted byproducts that are insoluble in the solvent (as low adducts,for example), are then filtered out.

Second, the filtered first reaction product is hydrolyzed with basessuch as, for example: MOH, where M is an alkali; carbonates such asM₂CO₃, wherein M is an alkali; or carbonates such as MCO₃, wherein M isan alkali earth. This produces a second reaction product of the generalformula --fullerene-R_(F)-hydrolyzed molecule--. Additionally, afterthis hydrolyzing process, there remains an excess amount of base that isremoved from the second reaction product by chromatography.

Third, the second reaction product is then protonated to form a thirdreaction product of the general formula --fullerene-R_(F)-protonconductive functional group--. This is the target proton conductor ofthe present invention. The second reaction product may be protonated byany suitable method such as, for example, use of cation exchange, or theuse of a strong inorganic acid.

The following is a non-limiting example of the above-described method ofmaking a proton conductor.

First, one equivalent of C₆₀ was combined with 24 equivalents ofI—C_(F2)—CF₂—CF₂—O—CF₂—CF₂—SO₂F (a spacer-molecule precursor) and a 1:1C₆F₆/CS₂ solvent mixture. The amount of CS₂ was about 7.9 mm/mg C₆₀, andthe amount of C₆F₆ was the same. The solution temperature was thenraised to about 200° C. for about 94 hours, whereupon greater than 70%of the reactants were reacted. Because the C₆F₆/CS₂ solvent mixtureboils at about 50° C., this step was performed under a pressure higherthan atmospheric, as in an autoclave, for example. Within thespacer-molecule precursor, the I side was the docking side that, uponremoval of the I, became attached to the fullerene molecule. The SO₂Fside of the spacer-molecule precursor would then undergo furtherreaction, in later steps, thus transforming it into a proton conductivefunctional group. If the solvent includes only C₆F₆, which precipitatesthe fullerenes, such would result in an unduly high percentage of C₆₀left unreacted. Therefore, the solvent also included a component, suchas CS₂, in which the fullerene dissolves. But the first reaction productis soluble in C₆F₆ and, therefore, such was also used to make it easy toseparate the first reaction product from the unreacted C₆₀.

Neither the temperature, nor the reaction time are critical, and canvary depending upon circumstances. Therefore, as long as the reaction iscarried out, higher temperatures can be used with shorter times and,similarly, lower temperatures can be used with longer times. In mostcases, a higher temperature will lead to a greater number of spacermolecules per fullerene. But in no case should the reaction temperatureexceed the temperature at which the spacer-molecule precursor begins todecompose. However, if too many spacer molecules are attached to thefullerene, then there are a reduced number of sites for attachment of alinking molecule during certain methods of polymerization, as discussedbelow. Also, if the reaction temperature is too high, undesirable sidereactions occur. Further, the more spacer molecules that are attached,then the more proton conductive groups there will be, which leads to anincreased proton conductivity but also to an increased water solubility(which is undesirable). Therefore, the temperature is selected to givean optimum balance of proton conductivity, and available sites forlinking molecules, while minimizing side reactions. If there are enoughsites for linking molecules, the polymer can be made water insolubleeven though a single proton conductor is water-soluble. The reactiontemperature can be achieved by heating. Alternatively, instead of or inaddition to heating, other suitable activation energies can be used suchas, for example, light energy such as visible or ultraviolet light.Thus, for the above-described exemplary reaction, the preferredtemperature range is from about 190° C. to about 240° C., with areaction time of about 94 hours.

The result of the first step, in this exemplary embodiment, was aplurality of first reaction products of the formulaC₆₀—(CF₂—CF₂—O—CF₂—CF₂ SO₂F)_(n) and about 5% to about 7% unreacted C₆₀(unless stated otherwise, all letters represented in subscript orsuperscript represent natural numbers). The unreacted C₆₀, and otherunwanted byproducts that were insoluble in the solvent, were thenfiltered out.

Second, the first reaction products C₆₀—(CF₂—CF₂—O—CF₂—CF₂ SO₂F)_(n)were hydrolyzed by reacting them with NaOH in a hydrolyzing step. Thesolution used in this step, to hydrolyze the first reaction product,included C₆F₆, THF, and NaOH. The C₆F₆ was used to get the firstreaction product into solution, because a dry first reaction productdoes not dissolve readily in THF. The amount of C₆F₆ can vary, there isno strict proportion, as long as there is enough to form a solution withthe first reaction product. However, water is completely insoluble inC₆F₆. Therefore, in order to get both the NaOH, and the first reactionproduct into solution, THF was used in combination with the C₆F₆, thefirst reaction product, and the NaOH. As preferred, the solution used inthis step included just enough C₆F₆ to get the first reaction productinto solution, an amount of THF that was equal to about 10 to about 20times the volume of the first reaction product in C₆F₆, and about 1/10to 1/20 of the Volume of C₆F₆+THF of 1 mol/liter of NaOH per oneequivalent of fullerene (C₆₀ in this exemplary embodiment). The smallestamount of NaOH that is conceivable (assumed a 100% reaction) is one NaOHper one —SO₂F group, i.e., with estimated eight —Rf—SO₂F adductsattached per C₆₀ it is at least 8 eq. However, since it is easier onewill always work with an excess of NaOH high enough to assure 100%hydrolyzing and low enough to easily remove the excess NaOH. Becausestrict proportions are not necessary to carry out this reaction, thismethod easily can be scaled-up, thereby facilitating production of theproton conductors in large quantities. The hydrolyzing step produced aplurality of second reaction products, each of the general formulaC₆₀—(CF₂—CF₂—O—CF₂—CF₂—SO₃Na)_(n), where n is a natural number, alongwith water and excess NaOH.

If the second reaction product and the byproducts (including excessNaOH) are run through a silica gel column using water only, then theresulting solution will be basic, but this is undesirable. Therefore,the solution was run through a silica gel column including THF andwater, in a 1:1 ratio, to remove the excess NaOH and to produce aneutral solution that includes the desired second reaction products,which are very water-soluble. At this point, the solvent (THF and water)was removed.

Third, the second reaction product was protonated to form a thirdreaction product, i.e., a target compound. After the solvent had beenremoved in the above step, a solution was made with the second reactionproducts and water. This solution was then put over an ion exchangecolumn, wherein H was substituted for Na in each of the second reactionproducts, thereby forming a plurality of the third reaction productshaving the general formula C₆₀—(CF₂—CF₂—O—CF₂—CF₂—SO₃—H)_(n), where n isa natural number.

The protonation can be performed by: a cation exchanger; by employing astrong inorganic acid such as HCl, H₂SO₄, HClO₄, or HNO₃; or any othersuitable method. These third reaction products were excellent protonconductors having a thermal and chemical stability greater than that ofthe fullerene-based proton conductors discussed in the background of theinvention. However, these proton conductors were very soluble in water.Therefore, in order to use these proton conductors in a fuel cellwherein water is present, it is beneficial to polymerize the protonconductors in order to increase their stability in water.

Although the number n is currently not controllable, when the fullereneis C₆₀, the average number of n throughout the above-describedexemplary-embodiment steps is about 6 to about 8, which gives goodproton conductivity. Also, about 6 to about 8 spacer molecules per C₆₀fullerene allows a sufficient number of sites on the C₆₀ fullerene forlinking molecules that are used to polymerize the proton conductors incertain polymerization methods.

In this exemplary embodiment, the third reaction product showed adecomposition temperature (as measured by TPD) of about 170° C. to about180° C., which is higher than that of compound 6 (100-110° C.) in FIG.4F. Additionally, the third reaction product showed a protonconductivity (2.4×10⁻⁵ at 20° C., 2.0×10⁻³ at 85° C., 1.1×10⁻³ at 95°C., and 7.9×10⁻⁴ at 105° C., all in S/cm) higher than that of compound 6(2.1×10⁻⁶ at 20° C., 4.8×10⁻⁴ at 85° C., 3.8×10⁻⁴ at 95° C., and3.4×10⁻⁴ at 105° C., proton conductivity data is measured in S/cm) inFIG. 4F, wherein conductivity was measured after drying the samplesovernight at 50° C. in an oil pump vacuum (producing about 0.001 mbar).Although the third reaction product's decomposition temperature was lessthan that of Nafion, such was also measured for the third reactionproduct as a molecule whereas that of Nafion was measured for a polymer.Therefore, the comparison is not an entirely true one, and one wouldexpect the third reaction product to show an increased stability whenused as a polymer. Also, when used in the form of a polymer, the protonconductors will desirably become water insoluble.

In order to use the proton conductors of the present invention in apolymer framework, they are cross-linked by cross-linking molecules. Across-linking molecule includes one, and preferably more than one, ofthe following characteristics: a fully, or partly, fluorinated molecule;an alkyl and/or aryl group; a length longer than that of the protonatedspacer molecule; and other functional groups such as ethers, esters,amides, and/or ketones.

As noted above, for certain polymerization methods, it is beneficial tobalance the number of cross-linking molecules per fullerene with thenumber of spacer molecules (which, in turn, are linked to the protonconductive function groups) per fullerene so as to achieve anoptimization of proton conductivity as well as thermal and chemicalstability (including water insolubility) of the polymer as a whole. Thepolymerization may be carried out as an additional step, between thefirst step of attaching a spacer-molecule precursor to a fullerene, andthe third step of protonating the spacer-molecule precursor.Alternatively, the polymerization may be carried out in a one-potreaction along with the first step of adding a spacer-molecule precursorto the fullerene.

As an example of polymerization by an additional step, the followingprocess may be used in connection with the above-described exemplaryprocess of making a proton conductor. Once the first reaction product,for example, C₆₀—(CF₂—CF₂—O—CF₂—CF₂ SO₂F)_(n) is produced, it is thenreacted with a bifunctional linking-molecule precursor of the generalformula:X—R—X, wherein:

-   -   X is Cl, Br, or I; and    -   R is a molecule having one or more of the following        characteristics: an alkyl and/or aryl group: fully, or partly,        fluorinated; a length longer than that of the protonated spacer        molecule; and other functional groups such as, for example,        ethers, esters, amides, ketones, and acid functional groups.

The bifunctional molecule, upon reacting with the first reactionproduct, forms bonds between fullerene molecules, thereby acting as alinking molecule to link two fullerene molecules together into apolymer. See FIG. 5 for a schematic representation of thispolymerization method and a polymer formed of proton conductors,according to this embodiment of the present invention. As shown in FIG.5, the fullerenes 30 have proton-conductive-group precursors 34 attachedthereto by spacer molecules 32. The proton-conductive-group precursors34 are —SO₂F, whereas the spacer molecules 36 are CF₂—CF₂—O—CF₂—CF₂.Linking molecules 36 connect the fullerenes 30 into a polymer, whereinthe linking molecules 36 are —(CF2)_(n)— and n is a natural number of 6or more, preferably 6 or 8. This reaction is carried out with asufficient activation energy to make the reaction work, wherein theactivation energy can be achieved by any suitable manner such as, forexample, the addition of heat, UV light, visible light, and the like.The polymer is then protonated as described above.

In an exemplary embodiment of the method of forming a polymer matrix ofproton conductors, 100 mg of the first reaction productC₆₀—(CF₂—CF₂—O—CF₂—CF₂ SO₂F)_(n) was reacted with excesslinking-molecule precursor I—(C₈F₁₆)—I.

Although I—(C₈F₁₆)—I was used as the linking-molecule precursor forC₆₀—(CF₂—CF₂—O—CF₂—CF₂ SO₂F)_(n), I(—(C_(n)F_(2n))—I could also be used,wherein n is a natural number of 6 or more, as such would produce alinking molecule longer than the protonated spacer. Generally, the morefluorine atoms that are present in the linking molecule, the more waterinsoluble the polymer network will be. But stability also depends on thepositions of F and H atoms in the case of a partially fluorinatedlinking molecule precursor. Further, instead of having an iodine atom oneither end of the linking-molecule precursor, it is also possible to useother halogens such as, for example, chlorine or bromine. The mainconsideration for selecting a linking-molecule precursor is that suchshould include one or more of the following properties: produces alinking molecule having water insolubility; produces a linking moleculethat has high stability in the thermal and chemical environmentstypically found in a fuel cell; produces a linking molecule that hasability to form a self standing film; at least two docking sites; andeasy reactivity with fullerene molecules. Further, although any lengthlinking-molecule precursor could be used, it is preferable to have thelinking-molecule precursor be such that it produces a linking moleculethat is longer than the protonated spacer molecule.

For this example, the (C₈F₁₆) linking molecule was selected because itis stable in the thermal and chemical environments found in a typicalfuel cell, has an ability to produce self standing films, provides waterinsolubility. Further, such linking molecule was selected because theprecursor molecule I—(C₈F₁₆)—I is commercially available, easily reactswith C₆₀, and produces a linking molecule that is longer than theprotonated spacer molecule produced by the I—CF₂—CF₂—O—CF₂—CF₂SO₂Fspacer-molecule precursor as used in the above-described exemplaryembodiment of the method for forming a proton conductor.

As an example of polymerization by a one-pot reaction, the followingprocess may be used in connection with the above-described exemplaryprocess of making a proton conductor. During the first step of producingthe first reaction product C₆₀—(CF₂—CF₂—O—CF₂—CF₂—SO₂F)_(n), asimultaneous reaction is carried out with a bifunctionallinking-molecule precursor of the general formula:X—R—X wherein:

-   -   X is Cl, Br, or I; and    -   R is a molecule having one or more of the following        characteristics: an alkyl and/or aryl group; fully, or partly,        fluorinated; a length longer than that of the protonated spacer        molecule: and other functional groups such as, for example,        ethers, esters, amides, ketones, and acid function groups.

That is, fullerenes are reacted with both spacer-molecule precursors,and with the bifunctional linking-molecule precursors simultaneously toform first reaction products that are linked together into a polymer.Again, this reaction is carried out with a sufficient activation energyto make the reaction work, wherein the activation energy can be achievedby any suitable manner such as, for example, the addition of heat, UVlight, visible light, and the like. See FIG. 6 for a schematicrepresentation of this polymerization method and a polymer formed ofproton conductors. As shown in FIG. 6, fullerenes 30 haveproton-conductive-group precursors 34 attached thereto by spacermolecules 32. Linking molecules 36 connect the fullerenes 30. The firstreaction products that are linked together into a polymer are thenhydrolyzed, and protonated to form a proton conductive polymer.

In an exemplary embodiment of this one-pot method of forming a polymernetwork of proton conductors, 357 mg of C₆₀ in 40 ml CS₂ was mixed with40 ml C₆F₆, 5.0 g of I—CF₂—CF₂—O—CF₂—CF₂—SO₂F (i.e., 24 equivalents),and 7.77 g I—(CF₂)₈(i.e., 24 equivalents).

The solution was then heated in an autoclave to 200° C. for 96 hours.After cooling the reacted mixture, the solvent was removed, therebyforming a cross-linked first reaction product.

The cross-linked first reaction product was then hydrolyzed as follows.The cross-linked first reaction product was put into solution with 5 mlC₆F₆, was diluted with about 85 ml THF, and was stirred overnight with 6ml of 1 M NaOH. After phase separation, the fullerene-containing organiclayer—in contrast the non-cross linked, and thus water soluble,fullerene sodium sulfonate is exclusively present in the aqueouslayer—was filtered through a short silica gel column (with THF as aneluent) in order to remove any remaining NaOH. Thehydrolyzed-cross-linked first reaction product obtained after removingthe solvent was water insoluble but was soluble in less polar solventslike methanol, THF, etc.

The hydrolyzed-cross-linked first reaction product was then dissolved in20 ml MeOH, was diluted with 80 ml H₂O (no precipitation was observedusing this solvent mixture), and was protonated via an ion exchangecolumn.

After drying overnight at 80° C., 1.8 g of acidic water-insolublematerial was obtained. This was the target proton conductive polymer.

For large reaction amounts, in either the additional step or one-potmethods, it may be advisable to add an additional purification stepafter the step of adding activation energy. The additional purificationstep is useful in removing the iodine that is formed along with theproduct in the reaction since large amounts of I₂ cannot be removedsimply by heating the material in vacuo. An example of this additionalpurification step is as follows.

To purify the compound a C₆F₆/THF solution was shaken out with 1M sodiumthiosulfate (Na₂S₂O₃) in H₂O. The C₆F₆/THF solution was preparedanalogously to the one used for the hydrolyzation of thefullerenesulfonyl fluoride with 1 M NaOH. Removing the salts was simplebecause the system C₆F₆/THF/1M Na₂S₂O₃ was a two-phase system in which,after the reaction, the salts, i.e., excess Na₂S₂O₃, NaI, and Na₂S₄O₆(the latter two being formed by reaction of sodium thiosulfate withI₂—were in the water layer. The organic phase containing the iodine-freefullerene sulfonyl fluoride was separated, the solvent was removed, andthe material was dried overnight in vacuum (0.001 mbar) at 120° C.

Again, although I—(C₈F₁₆)—I was used as the linking-molecule precursorfor C₆₀—(CF₂—CF₂—O—CF₂—CF₂—SO₂—F)_(n), I—(C_(n)F_(2n))—I could also beused, wherein n is a natural number of 6 or more, as such would producea linking molecule longer than the protonated spacer. In fact, for theone-pot reaction polymerization method, the linking-molecule precursorI—(C₆F₁₂)—I is preferred over I—(C₈F₁₈)—I, because the former produces ahigher conductivity in the polymer. Further, instead of having an iodineatom on either end of the linking-molecule precursor, it is alsopossible to use other halogens such as, for example, chlorine orbromine. Again, the main consideration for selecting a linking-moleculeprecursor is that such should include one or more of the followingproperties: produces a linking molecule having water insolubility;produces a linking molecule having high stability in the thermal andchemical environments typically found in a fuel cell; produces a linkingmolecule having an ability to form self standing films; at least twodocking sites; and readily reacts with fullerene molecules. Further,although any length linking-molecule precursor could be used, it ispreferable to have the linking-molecule precursor be such that itproduces a linking molecule that is longer than the proponated spacermolecule.

For this example, (C₈F₁₆) linking molecule was selected because it isstable in the thermal and chemical environments found in a typical fuelcell, has an ability to produce self standing films, provides waterinsolubility. Further, such linking molecule was selected because theprecursor molecule 1-(C₈F₁₆)—I is commercially available, easily reactswith C₆₀, and produces a linking molecule that is longer than theprotonated spacer molecule produced by the I—CF₂—CF₂—O—CF₂—CF₂—SO₂Fspacer-molecule precursor as used in the above-described exemplaryembodiment of the method for forming a proton conductor.

As an alternate example of polymerization by an additional step, and asan example of protonation by strong acid, the following process may beused.

First, once the first reaction product C₆₀—(CF₂—CF₂—O—CF₂—CF₂—SO₂F)_(n)is produced, it is then reacted with a bifunctional trimethylsilyl amidelinking-molecule precursor of the general formula:

R¹ is Li, Na, K, or Si—R² ₃; and

R² is an alkyl.

The bifunctional molecule, upon reacting with the first reactionproduct, forms bonds between spacer-molecule precursors that areattached to the fullerene, thereby acting as a linking molecule to linktwo fullerene molecules together into a polymer. This reaction iscarried out with a sufficient activation energy to make the reactionwork, wherein the activation energy can be achieved by any suitablemanner such as, for example, the addition of heat, UV light, visiblelight, and the like. Further, this reaction is carried out in solventslike THF, dioxane, acetonitril, perfluoro benzene, or any other solventcapable of forming solutions with the respective reagents. The reactioncan be performed at room or elevated temperatures and under atmosphericor elevated pressures, leading to second reaction products of thegeneral formula:[R_(f)-Fullerene-CF₂CF₂OCF₂CF₂SO₂NR¹SO₂CF₂CF₂OCF₂CF₂-Fullerene-R_(f)],wherein:

$\begin{matrix}{R_{f}\mspace{14mu}{is}\mspace{14mu}{``{{—CF}_{2}{CF}_{2}{OCF}_{2}{CF}_{2}{SO}_{2}F}"}} \\{{—CH}_{2},{{CF}_{2}{OCF}_{2}{CF}_{2}{SO}_{2}{NH}_{2}},{{and}\text{/}{or}}} \\{{—CF}_{2}{CF}_{2}{OCF}_{2}{CF}_{2}{SO}_{2}{NR}^{1}{{Si}R}_{3}^{2}\mspace{14mu}{and}\text{/}{or}} \\{{—CF}_{2}{CF}_{2}{OCF}_{2}{CF}_{2}{SO}_{2}{NR}^{1}{SO}_{2}{CF}_{2}{CF}_{2}{OCF}_{2}{CF}_{2}{—C}_{60}\text{-}{R_{f}.\mspace{14mu}{and}}\text{/}{or}} \\{{—CF}_{2}{CF}_{2}{OCF}_{2}{CF}_{2}{SO}_{2}{NR}^{1}{SO}_{2}{CF}_{2}{CF}_{2}{OCF}_{2}{CF}_{2}{—C}_{60}}\end{matrix}$

That is, unlike the bifunctional linking-molecule precursors of theprevious two examples, this bifunctional linking molecule-precursorforms a linking molecule between spacer-molecule precursors that areattached to the fullerene; i.e., it does not attach to the fullerenesthemselves. There can be, and generally are, two or more R_(f) moleculesper fullerene. Therefore, the products of this first step are—SO₂NR¹SO₂— linked fullerene subunits that bear various numbers ofunreacted R_(f) groups, wherein the R_(f) groups includesulfonylfluoride sites as well as possible side products likesulfonamide and —SO₂NR¹SiR² ₃.

Second, the sulfonyl fluoride functional groups on the second reactionproducts are hydrolyzed by using bases such as, for example: MOH,wherein M is an alkali; carbonates (M₂CO₃, wherein M is an alkali; MCO₃,wherein M is an earth alkali whereby third reaction products are formedand have the general formula:[R_(f2)-Fullerene-CF₂CF₂OCF₂CF₂SO₂NR¹SO₂CF₂CF₂OCF₂CF₂-Fullerene-R_(f2)],wherein:

$\begin{matrix}{{R_{12}\mspace{14mu}{is}{\mspace{14mu}}{—CF}_{2}{CF}_{2}{OCF}_{2}{CF}_{2}{SO}_{3}M},} \\{{{—CF}_{2}{CF}_{2}{OCF}_{2}{CF}_{2}{SO}_{2}{NH}_{2}},} \\{{—CF}_{2}{CF}_{2}{OCF}_{2}{CF}_{2}{SO}_{2}{NR}^{1}{{Si}R}_{3}^{2}\mspace{14mu}{and}\text{/}{or}} \\{{—CF}_{2}{CF}_{2}{OCF}_{2}{CF}_{2}{SO}_{2}{NHSO}_{2}{CF}_{2}{CF}_{2}{OCF}_{2}{CF}_{2}{—C}_{60}\text{-}R_{f\; 3}}\end{matrix}$

This reaction step may be performed in aqueous solutions of the bases,or in mixtures with organic solvents. The latter may form a one-phase ora two-phase system with the former. Elevated temperatures may beemployed. See FIG. 7 for a schematic representation of thispolymerization method and a polymer formed of proton conductors. Asshown in FIG. 7, fullerenes 30 having proton-conductive-group precursors34 attached thereto by spacer molecules 32 are combined withtrimethylsilyl amides (—R² ₃—Si—N—R¹—Si—R² ₃—) to form a polymer offullerenes 30 linked by sulfonyl imide linkage 38 that is

That is, the basic unit of the polymer is of the general formula[fullerene-spacer molecule-sulfonyl imide linkage-spacermolecule-fullerene].

Third, the third reaction products are protonated. For example, thethird reaction products may be protonated by using an ion exchanger orstrong inorganic acids like HCl, H₂SO₄HClO₄, HNO₃, and the like. Thisreaction can occur at room or elevated temperatures, whereby theresulting, desired, polymer is of the general formula:[R_(f3)-Fullerene-CF₂CF₂OCF₂CF₂SO₂NHSO₂CF₂CF₂OCF₂CF₂-Fulterene-R_(f3)]wherein:R_(f3) is —CF₂CF₂OCF₂CF₂SO₃H, or

—CF₂CF₂OCF₂CF₂SO₂NHSO₂CF₂CF₂OCF₂CF₂—C₆₀—R_(f3), and/or

—CF₂CF₂OCF₂CF₂SO₂NHSO₂CF₂CF₂OCF₂CF₂—C₆₀

In contrast to the two other above-described methods of polymerization,in this method the cross-linking is achieved not by employing extralinking units, but by using the acid precursor (i.e., the —SO₂Ffunctional group) as a docking site. The resulting sulfonyl imide(—SO₂NHSO₂—) itself shows strong acidity and can function as aproton-delivering site for H⁺ conductivity. Non-reacted sulfonylfluoride(—SO₂F) left over from the first reaction step, as well as side productspossibly obtained (i.e., —SO₂NH₂, —SO₂NR¹SiR² ₃) are converted intosulfonic acid groups during the course of the synthesis and contributeto the proton conductivity. Preliminary measurements shown high H⁺conductivity up to the order of 10⁻² S/cm at room temperature dependingon the amount of water contained in the solid. The material is insolublein common solvents and in water, an important prerequisite forapplication in a fuel cell. Due at least in part to the at least partialfluorination of the spacer molecules of the first reaction products, thepolymer achieves high thermal as well as chemical stability. TPDmeasurements showed thermal stability up to at least 200° C., which ison the order of the stability achieved by Nafion.

In an exemplary embodiment of this method of forming a polymer networkof proton conductors, the following steps were carried out.

In the first reaction step, 0.5 ml of a 1 M THF solution of

were added drop wise in an N₂ atmosphere and under ice cooling to 0.2 gof solid first reaction products C₆₀—(CF₂—CF₂—O—CF₂—CF₂—SO₂F)_(n) andstirred at room temperature for 5 hours. A dark brown precipitate wasformed and dried in vacuo at 60° C. for 3 hours. The resulting solid wasdissolved in 8 ml dioxane and 0.1 g of first reaction productsC₆₀—(CF₂—CF₂—O—CF₂—CF₂—SO₂—F)_(n) in 2 ml THF were added via a droppingfunnel. Then, after reflux for 18 hours, the solvent was removed and theobtained solid was washed with THF and water, resulting in 0.13 g ofsecond reaction products as described above.

In the second reaction step, hydrolysis, the second reaction productswere dispersed in 1M aqueous NaOH, and stirred at room temperature for16 hours. After filtering, and washing with water, solid third reactionproducts remained.

In the third reaction step, protonation, the solid third reactionproducts were heated with 10% HCl to 60° C. for 12 hours. Afterfiltering, and subsequent washing with 10% HCl and water, the desiredproton conductive polymer was attained.

As described above, this method includes the use of first reactionproducts having perfluorinated spacers. However, the first reactionproducts may include partially fluorinated spacers instead.

The polymer according to this method can be used as a proton conductorin fuel cells, electrolysis cells, and capacitors, for example. Thefullerene core may bear additional groups, such as: halides (F, Cl,and/or Br); alkyl and/or aryl groups; non, partially, or fullyfluorinated molecules; ethers; esters; amides; and/or keto functiongroups.

Further, the polymer may be used in combination with compounds capableof enhancing its proton conductivity in the absence of water. Forexample, the compounds may include polymers such as polyalkyl ethers,polyethylene carbonates, polyacryl amides, polyvinyl alcohols, andpolyethylene imines. Alternatively, or in addition to the polymers, thecompounds may include polar solvents such as alkyl carbonates, ethylenecarbonate, propylene carbonate, and the like. Still further, fully orpartly fluorinated derivatives of these compounds may be used.

Moreover, the polymer according to this method may be used as part of agel structure, such as a composite with silica gel. The gel may containadditional inorganic, or organic acids. The organic acids may be, forexample, HClO₄, H₂SO₄, H₃PO₄, dodecatungstophosphoric acid (H₃PW₁₂O₄₀×40H₂O), carboxylic acids, and the like.

The polymer framework of proton conductors according to the presentinvention may then be used as a proton exchange membrane in anelectrochemical device such as, for example, a fuel cell. A fuel cell isschematically shown in FIG. 2.

The fuel cell includes a first electrode 20, a second electrode 22, anda proton conductive membrane 24 disposed between the electrodes 20, 22.Conductors connect the electrodes 20, 22 to a load 26 such as, forexample, a light bulb, WALKMAN (Registered Trademark of SonyCorporation), an electrical or electronic appliance or device, anelectric circuit, and the like. When hydrogen (such as H₂) is suppliedto the first electrode 20, the hydrogen is broken down into protons (H⁺)and electrons (e). The electrons move along the conductors from thefirst electrode 20, drive the load 26, and then move on to the secondelectrode 22. Meanwhile, the protons move through the proton conductivemembrane 24 to the second electrode 22. The second electrode is suppliedwith oxygen such as, for example, in air or in another source of oxygen.Thus, when the protons and electrons arrive at the second electrode 22in the presence of oxygen, they recombine to form water (H₂O).

The proton conductive membrane 24 has a thickness of d. It is desirableto make d as thin as possible in order to achieve a fuel cell having aself-humidifying characteristic, as well as to reduce material cost. Asd decreases, the proton conductance increases, and the ability to easilyabsorb water increases. If d is thin enough, the water produced at thesecond electrode 22 will keep the membrane from drying out. Thisproduces a fuel cell with self-humidifying fuel cell, that is there isno need for an external source of humidity to keep the membrane moist.If the membrane dries out, it looses its ability to conduct protons andto prevent H₂ molecules from passing therethrough, i.e., the fuel cellwill not operate properly. Thus, the density of the membrane must not beso great as to prevent the absorption of water therein. Again, as thethickness d is decreased, there is an increase in the membrane's abilityto conduct protons. But this increased ability to conduct protons mustbe balanced by the necessity of the membrane to block passage of Hz. Ifthe membrane allows the H₂ to pass therethrough, then fewer electronsare produced and the efficiency of the fuel cell drops. Thus, themembrane's ability to pass protons and absorb water, while effectivelyblocking the passage of H₂, will determine its requisite thickness.

In a fuel cell having the polymer produced by the above-describedexemplary process (i.e., proton conductors having the general formulaC₆₀—(CF₂—CF₂—O—CF₂—CF₂—SO₃H)_(n) which are cross-linked by molecules of(C₈F₁₆), a membrane thickness of about 20 μm to about 30 μm havingacceptable proton conductivity on the order of 10⁻³ S/cm—produces aself-humidifying fuel cell that has an excellent conductance.

By way of example and not limitation, the proton conductivity ofperfluorohexyl cross-linked materials according to an embodiment of theinvention was measured as described in Measurements I to III below.

Measurements I and II:

Water uptake of the materials as depicted in FIG. 5 (n=6) (hereinafterMaterial FIG. 5 (n=6) and the material depicted in FIG. 6 (n=6)(hereinafter Material FIG. 6 (n=6)) were measured at differenttemperatures (19° C. and 50° C.). Before the measurements, the followingpretreatments were effected.

Pretreatment for measurement I: Dried overnight at a room temperature(19° C.) in a dry air stream (15% humidity).

Pretreatment for Measurement II: Dried overnight at 50° C. in a dry airstream (1.3% humidity).

At t=0 in FIGS. 8 and 9, the dry air stream was replaced by a watersaturated air stream, and the conductivity versus the time afterswitching from the dry air stream to the water saturated air stream wasrecorded. Measurements were taken for a temperature of T=19° C.(measurement I) as shown in FIG. 8, and for T=50° C. (measurement II) asshown in FIG. 9.

As indicated by the results of FIGS. 8 and 9, the materials exhibitedfast water uptake.

Measurement III:

The proton conductivity at various temperatures was measured. Also, therelative air humidity (R.H.) was registered in order to see theinfluence of the R.H. on the proton conductivity. As shown in FIG. 10,the material as depicted in FIG. 5 (n=6) (i.e., Material FIG. 5 (n=6))was shown to be less prone to humidity changes than the materialdepicted in FIG. 6 (n=6) (i.e., Material FIG. 6 (n=6)).

Measurements I to III, as described above, in general show that thematerial prepared by a two-step process (Material FIG. 5 (n=6)) exhibitsproton conductivity at about two orders of magnitude higher than thematerial prepared by the one-step process (Material FIG. 6 (n=6)). Thesame conditions were present when the two samples were measured.

Perflourinated cross-linked materials based on C₇₀ were also preparedand tested using reaction conditions similar to those described abovefor the method of preparing cross-linked materials using C₆₀. Morespecifically, one equivalent of C₇₀ was combined with 24 equivalents ofI—CF₂—CF₂—O—CF₂—CF₂—SO₂F as the spacer-molecule precursor and a 1:1C₆F₆/CS₂ solvent mixture. The solution temperature was then raised toabout 240° C. for about 94 hours, whereupon greater than 70% of thereactants were reacted (essentially the same yield as when using C₆₀).The higher reaction temperature used for C₇₀ (240° C.) versus thetemperature for C₆₀ (200° C.) can be attributed to the lower reactivityof C₇₀ as compared to C₆₀. The remaining steps of making theperflourinated cross-linked materials based on C₇₀ are the same as thosedescribed using C₆₀. FIG. 11 shows the proton conductivity at varioustemperatures for samples of the materials based on C₇₀, as well as acomparison of the these C₇₀ based samples with a respective C₆₀ basedsample and a Nafion sample. The relative air humidity (R.H.) was alsomeasured in order to see the influence of the R.H. on the protonconductivity.

In this example, from t=−280 min. until t=0, the measurement chamber waspurged with dry air. As shown in FIG. 11, during this time, theconductivity of the C₇₀ based samples decreased less than the C₆₀ basedsample, and one C₇₀ based sample (C₇₀(Rf—SO₃H)10/PVA) showed improvedbehavior when compared to the Nafion sample. At t=0, the dry air streamwas replaced by a water saturated air stream which resulted inincreasing the conductivity of the samples. FIG. 11 indicates that theC₇₀ based samples were less prone to humidity changes than the C₆₀ basedsample and the Nafion based sample (at least in a case using a PVAmembrane).

To further decrease the humidity sensitivity of the proton conductors ofthe present invention, short linkers may be used as the spacer module toconnect the acidic group (the proton conductive function group) with thefullerene core. For example, the linker used in CF₂CF₂OCF₂CF₂SO₃H has alength of about 8 Å, while the linker used in CF₂SO₃H has a length ofabout 3 Å. Synthesis of materials using short linkers (in combinationwith C₆₀ or C₇₀, for example) and methods to turn them insoluble (e.g.,cross-linking using perfluoro alkanes and the sulfonimide linkage andthe use of binders (for example, PVA)) are as described herein. Usingthe short linkers allows for a higher volume density of acidic groups inmaterials (more acidic groups per cm³) which should keep water bettersince the acidic groups form the hydrophilic part of the materials. Thishigher interaction with water means that the materials are less prone tohumidity changes. Also, the molecules using the short linkers are mademuch lighter. For example, when using longer linkers with a fullerenecore of C₆₀, one acidic group has an EW-value of 390 mass units while asecond acidic group using short linkers with a fullerene core of C₆₀ hasan EW-value of 220 mass units. This results in higher conductivity ofmaterials using the shorter linkers. Shorter linkers may lower theEW-value below 220 mass units. Also, the denser packing allowable as aresult of these short linkers makes it possible to reduce leaking offuel when the proton conductors of the present invention with shortlinkers are employed in a fuel cell device.

The present invention provides a proton conductive compound that has ahigh conductivity, and that is thermally as well as chemically stableunder conditions found in a fuel cell.

The present invention provides a novel fullerene-based proton conductivematerial combining the advantages of the most widely used protonconductor Nafion, with the benefits of employing a spherical-typefullerene backbone.

Additionally, the present invention achieves a high proton conductivitybecause these fullerene-based proton conductors have a high number ofproton conductive groups per unit of atomic weight. Further, thefullerene-based proton conductors of the present invention have at leasta partially fluorinated spacer molecule connecting a proton conductivefunctional group to the fullerene back bone, whereby the presentinvention achieves a higher thermal and chemical stability than that ofthe fullerene-based proton conductors previously known withinApplicants' company.

Also, the present invention achieves cross-linked materials havingrelatively low humidity sensitivity by using short linkers to connectthe acidic groups with the fullerene core.

Further, the present invention provides methods of manufacturing theabove-described proton conductor, as well as a polymer film thereof. Themethods provide reactions in which strict proportions are unnecessary.Therefore, these methods easily can be scaled-up to make largequantities of proton conductors and of proton-conductive polymers.

The present invention provides—due to use of the above-described protonconductive polymer as a proton exchange membrane—an electrochemicaldevice having an acceptable conductance, and self-humidifyingcharacteristics, as well as an increased thermal and chemical stability.

It is contemplated that numerous modifications may be made to the protonconductor, polymer, methods of making the proton conductor and polymer,and the electrochemical device including the proton conductor, of thepresent invention without departing from the spirit and scope of theinvention as defined in the claims.

It should be understood that various changes and modifications to thepresently preferred embodiments described herein will be apparent tothose skilled in the art. Such changes and modifications can be madewithout departing from the spirit and scope of the present invention andwithout diminishing its intended advantages. It is therefore intendedthat such changes and modifications be covered by the appended claims.

1. A proton conductive polymer comprising: a plurality of protonconductors, each comprising a fullerene molecule, a spacer moleculecomprising an at least partially fluorinated molecule attached to saidfullerene molecule, a proton conductive functional group attached tosaid spacer molecule, and at least one linking molecule connectedbetween two of said plurality of proton conductors; and a compoundcapable of enhancing proton conductivity in the absence of water.
 2. Theproton conductive polymer of claim 1, wherein said linking molecule isconnected to the spacer molecules of at least two of said protonconductors.
 3. The proton conductive polymer of claim 2, wherein atleast one fullerene of at least two of said proton conductors hasattached thereto an additional functional group selected from the groupconsisting of an alkyl group, an aryl group, a non-fluorinated moleculargroup, a partially fluorinated molecular group, a perfluorinatedmolecular group, an ether group, an ester group, an amide group, a ketogroup and combinations thereof.
 4. The proton conductive polymer ofclaim 2, wherein said linking molecule is selected from the group of apartially fluorinated, a perfluorinated, sulfonylimide molecule andcombinations thereof.
 5. The proton conductive polymer of claim 4,wherein said linking molecule includes an additional functional groupthat is selected from the group consisting of ethers, esters, amides,keto groups and combinations thereof.
 6. The proton conductive polymeraccording to claim 1, wherein said compound is selected from the groupconsisting of polyalkyl ethers, polyethylene carbonates, polyacrylamides, polyvinyl alcohols, polyethylene imines, alkyl carbonates,ethylene carbonate, propylene carbonate, fully fluorinated derivativesthereof partially fluorinated derivatives thereof, and combinationsthereof.